1. Field of the Invention
The present invention relates to the field of radio or microwave frequency antennas; more specifically, the present invention relates to compact ceramic-embedded antennas suitable for use with apparatus using radio or microwave communication.
2. Description of Problem Sought to be Solved
Many portable devices in use today rely on radio communications to receive and transmit information. Examples of such devices include pagers, cellular telephones, automobile phones, wireless telephones, GPS (Global Positioning Satellite) receivers, portable terminals, personal computers, walkie talkies, baby monitors, and the like. This list is by no means exhaustive and the use of radio and microwave communications for portable devices can only be expected to grow. For example, it is proposed to develop a network of satellites that will make possible the linking of personal computers with the Internet from any place on earth.
Devices that use radio or microwave communications require antenna systems in order to couple their circuitry to the free space around them in order to receive and transmit information. In the past, wire or linear conductor antennas have been employed in such systems. Wire antennas may be coiled into helixes or spirals to reduce the overall length while maintaining a larger effective length. Such antennas frequently are in the form of dipole antennas in which the antenna forms one-half of the dipole and a circuit element, the casing or other metallic structure of the radio apparatus forms the other half of the dipole.
Wire or linear conductor antennas, however, are relatively large, bulky, and fragile. A need exists for antennas that are small, strong, and inexpensive, especially for use with the portable radio communication devices mentioned above.
Helical conductor antennas have been developed that are formed from laminated ferrite ceramic sheets bearing conductive segments on each sheet. The spiral conductive segments are electrically connected through the ferrite ceramic sheets in order to form the spiral conductive element, which is embedded or "potted" in the laminated ferrite ceramic sheets and is a quarter wavelength in effective length. See U.S. Pat. No. 5,541,610 to Imanishi, et al. for an "antenna for a radio communication apparatus." The antenna is miniaturized not only because it is helical but also because it is embedded in a ceramic material having a higher electrical permittivity (.di-elect cons.) and/or magnetic permeability (.mu.) than that of free space (.di-elect cons..sub.0,.mu..sub.0). It will be recalled that ##EQU1## wherein .lambda.=wavelength, c=speed of light in free space (vacuum), .nu.=frequency, .di-elect cons..sub.r =.sup..di-elect cons. /.di-elect cons..sub.0 =relative electrical permittivity or dielectric constant and .mu..sub.r =.sup..mu. /.mu..sub.0 =relative magnetic permeability of the medium of propagation. For a given frequency, an increase in the dielectric constant .di-elect cons..sub.r and/or the relative magnetic permeability .mu..sub.r decreases the wavelength of electromagnetic radiation in the medium of propagation. The necessary length of the antenna in such a ceramic material is thus reduced.
Previous ceramic embedded antennas have employed the control of magnetic permeability by using ferrite ceramics. The effective length of the spiral conductive elements of these antennas was adjusted by changing the physical size of the spiral conductive element.
A need exists for an improved helical antenna which has low total volume, small dimensions, high mechanical strength, and can be manufactured by inexpensive and high volume manufacturing process. Such an antenna should be readily manufactured to be compatible with radio or microwave frequencies currently in use and likely to be used in the future, without necessarily changing the physical size of the antenna.
A need also exists for devices using radio or microwave communications, especially portable devices, that have improved antennas with the characteristics set forth above.